Decorative fixture members have been used widely and generally in the field of building materials due to the demands for making structures and the like more attractive and achieving durability and the like. The decorative fixture members were obtained by pasting a sheet or a film such as a decorative sheet on which decorative color and/or a decorative pattern are formed, on a substrate such as plywood, MDF (medium density fiber board), a particle board and the like.
Substrates generally used for decorative fixture members tend to have complex portions, such as a groove or ditch portion, an “R” portion (the “R” stands for a round form, and the “R” portion means a portion such as a convex curved portion), a reverse “R” portion and the like. Accordingly, it is necessary for the adhesive used for pasting a sheet and a substrate together to have excellent adhesiveness such as that which can prevent peeling of the sheet or the like from complex portions of the substrate. As the aforementioned adhesive, an organic solvent type adhesive and a hot-melt adhesive including a thermoplastic resin as a main component have been used.
However, when the organic solvent type adhesive is used, it is necessary to remove the organic solvent therefrom by a method such as drying conducted in the middle of the manufacturing step of the decorative fixture member, and therefore there are many problems such as a high energy load for evaporating organic solvent, adverse effects on the human body, contamination of the atmosphere or water quality due to the organic solvent and the like. Furthermore, there is a problem that the surface smoothness of the obtained decorative fixture member deteriorates when a part of the organic solvent remains in an adhesive layer used for pasting a sheet or the like on a substrate. On the other hand, it may be possible to solve such problems caused by the organic solvent when the aforementioned hot-melt adhesive is used instead of the organic solvent type adhesive, since the hot-melt adhesive is a solvent-less type adhesive. However, there is a problem that a layer formed from the hot-melt adhesive cannot provide sufficient heat resistance, solvent resistance and the like.
In order to solve the aforementioned problems, various moisture-curable polyurethane hot-melt adhesives have been examined as an adhesive used for decorative fixture members. For example, it has been reported that sufficient adhesive strength can be achieved from the initial stage without decreasing the life of the adhesive after it has been pasted, wherein a moisture-curable polyurethane hot-melt adhesive is used, the adhesive includes a urethane prepolymer having a main chain skeleton formed from an amorphous polymerpolyol, the chain length of the skeleton is extended by specific low-molecular weight glycol and polyisocyanates, and an active isocyanate group exists at terminal ends thereof. For an example, please refer to patent document 1.
However, the adhesive strength which is achieved due to the near completion of a moisture-curing reaction (hereinafter, it is referred to as the “final adhesive strength”) of the aforementioned moisture-curable polyurethane hot-melt adhesive is insufficient.
Furthermore, there is a problem that when a sheet or the like is pasted on a substrate having complex portions such as a groove or ditch portion, an “R” portion, a reverse “R” portion and the like, partial peeling of the sheet or the like was caused at complex portions of the substrate within a period from when the sheet is applied to the substrate to until the final adhesive strength is achieved.
Furthermore, it has been reported that excellent initial adhesiveness is achieved due to the use of a moisture-curable polyurethane hot-melt adhesive including a polyurethane resin, which has an isocyanate group at both terminal ends and can be obtained by reacting crystalline aliphatic polyester diol, aromatic polyester diol and diisocyanate. For an example, please refer to patent document 2.
Furthermore, it has been reported that excellent viscosity stability at the time of melting, sufficient initial adhesive strength and sufficient final adhesive strength are achieved due to a moisture-curable polyurethane hot-melt adhesive for a wooden decorative member. The hot-melt adhesive comprises urethane prepolymer wherein the prepolymer is obtained by the reaction between organic polyisocyanate and polymerpolyol which includes crystalline polyol having a number average of 2,000 to 10,000 and amorphous polyol having a number average of 300 to 800. For an example, please refer to patent document 3.
Moreover, it has been reported that a mono-liquid moisture-curable polyurethane resin composition provides almost no reduction in elastic modulus even if heating is conducted subsequent to humidity curing, wherein the composition comprises urethane prepolymer obtained by the reaction between polyisocyanate and a mixture of polyol containing crystalline polyesterpolyol, amorphous polyesterpolyol and/or amorphous polyetherpolyol. These polyols in the resin composition are in a condition that they are mixed with each other due to compatibility. For an example, please refer to patent document 4.
However, even if any of the moisture-curable polyurethane hot-melt adhesives described in patent documents 2 to 4 are use, it is impossible to completely solve problems in that, when a sheet or the like is pasted on a substrate which has complex portions such as a groove or ditch portion, an R portion, a reverse R portion, and the like, unpreferable partial peeling of the sheet or the like is caused at the complex portions of the substrate within a period between the pasting of the sheet to the substrate and when the final adhesive strength is achieved. Furthermore, final adhesive strengths achieved by the adhesives of these documents are still insufficient.
In many cases, a conventional decorative fixture member is manufactured by a method such that adhesive is applied to a substrate or a sheet, the substrate and the sheet are put together, and then pressure is applied thereto for fixing. As a sheet or the like which is generally used in the method, a rolled sheet having connecting portions which exist every hundred meters is used in many cases. However, a decorative fixture member, in which a sheet or the like having a connecting portion is pasted on a substrate, serves as an inferior item, since the appearance of such decorative fixture members is poor. Accordingly, it is important to reduce such inferior items from the viewpoint of saving resources. Furthermore, it is particularly desirable to recycle a substrate by stripping the sheet or the like from a decorative fixture member when it become undesirable, since a substrate is more expensive than the sheet or the like.
However, conventional moisture-curable polyurethane hot-melt adhesives, which have been used for decorative fixture members, are adhesives which have been developed in order to improve initial adhesive strength to prevent the aforementioned problems of the peeling of the sheet or the like from a substrate. Accordingly, there are problems that when a sheet or the like is pasted on a substrate with the aforementioned adhesives, peeling of the sheet from the substrate is difficult after a predetermined period of time has passed, for example after about three minutes passed, it becomes difficult to peel the sheet or the like from the substrate. Furthermore, even if it is possible to peel the sheet or the like from the substrate, there is a problem that the substrate from which the sheet or the like was peeled cannot be recycled since remarkable unevenness is formed on the substrate by the peeling.    Patent document 1: Japanese Unexamined Patent Application, First Publication No. Hei 04-028783    Patent document 2: Japanese Unexamined Patent Application, First Publication No. Hei 05-051573    Patent document 3: Japanese Unexamined Patent Application, First Publication No. 2002-194318    Patent document 4: Japanese Unexamined Patent Application, First Publication No. 2003-327647